Stabilization of water soluble acetohydroxamic acid salts



United States Patent 3,419,603 STABILIZATION OF WATER SOLUBLEACETOHYDROXAMIC ACID SALTS Stanley A. Lipowski, Livingston, and CharlesA. Fetscher,

Short Hills, N.J., assignors to Diamond Shamrock Corporation, acorporation of Delaware No Drawing. Filed Sept. 1, 1964, Ser. No.393,774

4 Claims. (Cl. 260-5005) ABSTRACT OF THE DISCLOSURE Water soluble alkalimetal salts of acetohydroxamic acid are stabilized by treatment withformic and acetic acids. For example, to still liquid potassiumacetohydroxamate was added by weight of glacial acetic acid. Thestabilized salt was heated to 240 C. without exploding.

The present invention relates to a process for stabilizing water solublealkali metal salts of acetohydroxamic acid. More particularly, thepresent invention relates to treatment of water soluble alkali metalsalts of acetohydroxamic acid with acid thereby bringing about a new andhighly stable form of the aforesaid salts.

Acetohydroxamic acid and its alkali metal salts, because of thehydroxamic acid functional group would make an outstanding chelator forheavy metals such as copper, iron, cobalt, nickel, chromium, manganese,vanadium, uranium, gold, platinum, palladium and rhodium. That is, thelow molecular weights of these materials bring about a very highchelating capacity which is about 6.6 meq. per gram for theacetohydroxamic acid and from 4.5 to 5.5 meq. per gram for its alkalimetal salts. At tempts to isolate the free acid, we have found, involvecumbersome procedures. The free acid is therefore uneconomical toprepare and hence, has little chance of utility as a chelator. Regardingthe preparation of water soluble alkali metal salts of acetohydroxamicacid, these have not been previously isolated. We have isolated alkalimetal salts of acetohydroxamic acid, e.g., the potassium salt, which wefound exists in the form of a white crystalline mass. It, too, is achelator for heavy metals including those listed previously. However, wehave discovered that upon heating, the salts explode with a violentforce. In

view of this unsatisfactory property of the salts, their use aschelators is clearly quite limited.

Accordingly, it is an object of the present invention to prepare watersoluble alkali metal salts of acetohydroxamic acid in a highly stableform thereby allowing these salts to be used as chelators. Anotherobject of the present invention is to stabilize water soluble alkalimetal salts of acetohydroxamic acid in a novel manner thereby bringingabout a new and highly stable form of said salts characterized byenhanced stability, which renders same useful as chelators. A furtherobject is to provide for water soluble alkali metal salts ofacetohydroxamic acids which are stable when heated at elevatedtemperatures. Other objects will become apparent from the detaileddescription given herein. It is intended, however, that the detaileddescription and specific examples do not limit the invention, but merelyindicate preferred embodiments thereof since various changes andmodifications within the scope of the invention will become apparent tothose skilled in the art.

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We have discovered that the above and other objects may be achieved bytreating water soluble alkali metal salts of acetohydroxamic acid,preferably while in a liquid state, with acid. Upon solidification, ahighly stable material is obtained. We have found that especially usefulorganic acids are formic and acetic acids or their mixtures, preferablyglacial acetic acid. In order to achieve stabilization, the salts ofacetohydroxamic acid should be treated with at least about 0.1 mol ofacid per mol of salt. The maximum quantity of acid is not critical.However, we have found that usually there is no need to treat the saltswith more than about 0.6 mol of the acid per mol of salt. For example,when using glacial acetic acid, we can use from about 0.1 to about 0.6mol of glacial acetic acid per mol of salt, preferably about 0.2 mol ofglacial acetic acid per mol of salt. Larger quantities of acid, asindicated above, can be utilized. However, their use will not furtherenhance the stability of the salts. Although we prefer to add the acidto the salt of acetohydroxamic acid while the latter is in the liquidstate, that is, when it is in a molten state, e.g., before itsolidifies, stabilization can also be achieved to some degree when theacid is added to and mixed with the solidified salt.

It might appear that the successful stabilization of these salts is dueto the fact that the acids when introduced merely neutralize a certainquantity of the salt thereby damping or reducing the violence of theexplosion of the remaining salt upon heating, that is, a dilution effectis achieved. However, this is not the case at all because when physicalmixtures of salts of acetohydroxamic acid and free acetohydroxamic acidare prepared which correspond stoichiometrically to a partialneutralization based on the same amount of acid used herein, no enhancedstability is obtained. Therefore, it was most unexpected to discoverthat by treating the salts of acetohydroxamic acid with acid, a highlystable form of the salt was obtained. Thus, it is clear that bufferingor partially neutralizing the salts of acetohydroxamic acid brings aboutthermal stability in an unexpected manner which is not a simple dilutionor neutralization effect.

For a fuller understanding of the invention, reference may be had to thefollowing examples which are given merely as further illustrations ofthe invention and are not to be construed in a limiting sense.

EXAMPLE I.-Preparation of potassium acetohydroxamate 230 grams ofpotassium hydroxide pellets (85.4% KOH) were dissolved in 1200 cc. ofmethanol thereby forming a 2.89 normal solution. grams (2 mols) ofhydroxylammonium chloride were dissolved in 800 cc. of methanol. Then,690 cc. of the 2.89 normal potassium hydroxide solution were added withcooling to the hydroxylammonium chloride solution. The resulting mixturewas cooled down to 5 C. and the precipitated potassium chloride wasfiltered off. The pH of the filtrate was 8.0. The filtrate containedhydroxylamine in solution. 132 grams (1.5 mol) of ethyl acetate werethen added to the hydroxylamine solution. Thereafter, 345 cc. of the2.89 normal potassium hydroxide solution were added to the hydroxylaminesolution during the course of two hours. During this addition, the pHremained constant at 11.8 and the temperature rose from 22 to 35 C. Thereaction mixture was left standing overnight. Then, the methanol solventand the ethyl alcohol and water which were formed as by-products duringthe reaction were removed by vacuum distillation .at a pressure of 50mm. of mercury and at a maximum temperature of 75 C. The residue was aslight yellowish oil of potassium acetohydroxamate which upon slowcooling solidified to a white crystalline mass.

EXAMPLE II Approximately 20 grams of the potassium acetohydroxamate saltwhich was prepared in accordance with the procedure of Example I wereplaced in a 150 cc. beaker with a thermometer immersed in the salt. Thebeaker was heated slowly and carefully on a hot plate. When thetemperature reached 100 C., a sudden rise in temperature to 170 C. wasobserved and the salt exploded violently, shattering the immersedthermometer.

Similarly, when 20 grams of the same salt were placed in a 250 cc.round-bottom flask equipped with a thermometer and stirrer, the saltexploded violently upon heating to 100 C., shattering the flask, stirrerand thermometer.

EXAMPLE IIL-Stabilization of potassium acetohydroxamate To 22.6 grams(0.2 mol) of the still liquid potassium acetohydroxamate prepared in thesame manner as Example I were added 2.26 grams (0.037 mol) of glacialacetic acid. Upon cooling, this mixture solidified. The solidified, drymixture was heated up to 240 C. at which time the mixture started tochar slowly. No explosion occurred during this period of heating. Theamount of glacial acetic acid utilized in this example was about 0.19mol of acid per mol of salt, i.e., by weight of the salt. The pH of a50% solution in water of the mixture was 10.5. This solution was boiledfifteen minutes without any indication of decomposition.

EXAMPLE IV The stabilization procedure of Example III was repeated,however, 4.52 grams of glacial acetic acid were utilized instead. Thisamounted to about 0.38 mol of glacial acetic acid per mol of salt, i.e.,20% by weight of the salt. The dry mixture was heated to 240 C. withoutexplosion. The pH of a 50% water solution was 9.5.

EXAMPLE V The stabilization procedure of Example III was repeated exceptthat 6.78 grams of glacial acetic acid were utilized. This amounted toabout 0.57 mol of acid per mol of salt, i.e., 30% by weight of the salt.When the dry mixture was heated to a temperature of 240 C., no explosionoccurred. The pH of a 50% water solution was 7.5.

EXAMPLE VI Attempted Stabilization of Potassium AcetohydroxamateUtilizing a Physical Mixture (A) A mixture was prepared of the materialswhich would be present if our in-situ stabilization is merely a partialneutralization as shown as follows. In Example III, for instance, thestable composition was made by adding glacial acetic acid to potassiumacetohydroxamate in the following ratio:

Mol

Potassium acetohydroxamate 0.2 Glacial acetic acid 0.037

This blend, as observed, was stable up to 240 C., and even at thattemperature decomposed slowly without any violence. If this is simply apartial conversion of the explosive salt to the stable acid the systembecomes:

Mol Potassium acetohydroxamate 0.163 Free acetohydroxamic acid 0.037Potassium acetate 0.037

A mixture of these three materials was prepared exactly according to theproportions above. A portion of this mixture exploded violently whenwarmed to 100 C.

(B) A further portion of the above three component mixture was dissolvedin an equal weight of water. The pH of this solution was 10.0, actuallysomewhat lower than that of a 50% solution of the stable material ofExample III. If reduced alkalinity were the whole explanation ofstability, this material of Example VI should be slightly more stablethan that of Example III.

A part of the aqueous solution of the Example VI mixture was heated toits boiling point, i.e., about C. After a few minutes of boiling, thesolution exploded vigorously.

This is evidence that the stability we achieve by the addition of asmall amount of acid is not due solely to partial neutralization or todilution. Some complex and unexplained interaction must take place.

For Example III and Example VI, the molecular and material balance is asfollows:

EXAMPLE III M01 Grams Potassium acetohydroxamate 0. 2 22. 6 Acetic acid0. 037 2. 26

Total 0. 237 24. 86

EXAMPLE VI Mol Grams Potassium acetohydroxamate 0. 163 18. 4Acetohydroxamic acid 0.037 2. 8 Potassium acetate 0.037 3. 66

Total 0.237 24. 8

Our stabilization procedure is applicable to the sodium and lithiumsalts of acetohydroxamic acid as well as to the potassium salt set forthabove.

The following examples demonstrate the ability of our stabilized saltsto chelate metals.

EXAMPLE VII An aluminum oxide catalyst contaminated with 0.1% vanadiumoxide (V 0 was purified by washing with a 2% water solution of thepotassium acetohydroxamate stabilized as described in Example III above.The solution immediately turned purple in color indicating chelation ofthe vanadium by potassium acetohydroxamate and the washed catalyst wasfree from vanadium. Vanadium oxide is otherwise difiicult to removewithout damaging the catalyst.

EXAMPLE IX To a 1% cupric sulfate solution was added the stabilized saltof Example III. A copper complex precipitated in form of bright greenflocks which was very insoluble in water.

Having described our invention, what we claim as new and desire tosecure by Letters Patent is:

1. A process for stabilizing water soluble alkali metal salts ofacetohydroxamic acid comprising bringing together a wall soluble alkalimetal salt of acetohydroxamic acid while in a liquid, solvent free stateand from about 0.1 to 0.6 mol of glacial acetic acid per mol of saidsalt.

2. A process for stabilizing potassium acetohydroxamate which comprisesbringing together said salt while in References Cited UNITED STATESPATENTS 2,397,508 4/1946 Rouault et al. 260500 6 OTHER REFERENCES Yale:Chem. Rev., vol. 33, (1943), pp. 228 to 229.

Cambi: Ben, vol. 69 (1936), pp. 2027-33.

LEON ZITVER, Primary Examiner.

J. E. EVANS, Assistant Examiner.

US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,419,603 December 31, 1968 Stanley A. Lipowski et al.

pears in the above identified It is certified that error ap t are herebycorrected as patent and that said Letters Paten shown below:

Column 4, line 31, under column entitled "Grams" the total "24.8 shouldread 24.86 line 71, "wall" should read water Signed and sealed this 24thday of March 1970.

(SEAL) Attest:

Attesting Officer WILLIAM E. SCHUYLER, JR.

